A 35 y/o male is the driver of a vehicle observed to ‘drift’ off the shoulder of an interstate highway, and with no evidence of skid marks or braking. He s

 Case study #1 

A 35 y/o male is the driver of a vehicle observed to 'drift' off the shoulder of an interstate highway, and with no evidence of skid marks or braking. He strikes an abutment of a bridge at about 35 mph. The driver is belted, and airbags deploy. He is found to have no vital signs when paramedics arrive several minutes after the impact, and the patient is pronounced dead at the scene.
At the medical examiner's office, the body shows abrasions on the chest, and several fractured ribs with no associated contusions of the chest or internal hemorrhage of the chest or abdomen. A lacerated spleen and liver are also noted. No contusions, or subdural hemorrhages are present in the brain. There is a large subarachnoid hemorrhage seen and ruptured aneurysm of the anterior communicating cerebral artery is noted. 

1. What are the cause and manner of death?
2. What is the significance of the lack of internal hemorrhage in the abdomen and chest?
3. In many jurisdictions, this case would have been signed out as blunt force trauma due to automobile collision, and no autopsy would have been performed. In some jurisdictions this would have been done by a lay coroner. What are the advantages of doing an autopsy?